Electric power transmission is a process in the delivery of electricity to consumers. In general, the term “electric power transmission” refers to the bulk transfer of electrical power from place to place, for example, between a power plant and a substation near a populated area. Due to the large amount of power involved, electric transmission normally takes place at high voltage (110 kV or above). Transformers are used at the substations to step the voltage down to a lower voltage for distribution to commercial and residential users.
Major power transformers are filled with a fluid, typically of a mineral oil origin, that generally serves as a dielectric media, an insulator, and a heat transfer agent. During normal use this fluid typically undergoes a slow degradation to yield gases that collect in the oil. When there is an electrical fault within the transformer, these gases are generated more rapidly. Each of a number of fault conditions possible within a transformer generates certain key gases and a distribution pattern of these gases. Thus, the character of the fault condition giving rise to the gases can be ascertained by determining the various gases present in the transformer fluid and their amounts.
Dissolved gas analysis (DGA) is a widely used predictive maintenance technique for monitoring the collection and rate of generation of gases in transformer fluid, in order to gauge the operation of transformers. An appropriate dissolved gas analysis schedule can be set up depending on the location of a transformer, the nature of its usage, and the criticality of the unit. In addition, when a fault condition is detected the sampling frequency may be increased to determine how rapidly the gases are being generated and thus how serious the problem might be so that proper action can be taken before the unit suffers additional damage. In addition, it is considered essential to maintain a history of each unit so that a determination can be made as to whether any gases are residual ones from a previous fault condition or are they due to a newly developing fault condition.
On-line dissolved gas analysis units can provide analysis of multiple gases, for example, hydrogen (H2), oxygen (O2), carbon monoxide (CO), carbon dioxide (CO2), methane (CH4), acetylene (C2H2), ethylene (C2H4), and ethane (C2H6). Samples may be taken periodically, for example, every four hours, from each transformer being monitored. This sample rate desirably increases to, for example, hourly if predefined thresholds for an individual gas, or if a rate of change for an individual gas, is reached. At a utility managing many transformers, this sample rate yields a plethora of data samples, each of which is to be analyzed.
Human nature and workload can cause otherwise responsible individuals to postpone analysis of a group of samples due to the repetitive nature of the samples from the on-line DGA monitoring units. The usefulness of an on-line monitoring system can thus be defeated when the enormous quantity of data is not examined in a timely manner. Consequently, the utility is typically faced with too little information for a variety of apparatuses because it cannot adequately collect and filter the data into manageable and useful information. Under these circumstances, certain conditions can go undetected until a catastrophic event occurs.
Utilities are interested in safely maximizing the use of their assets, minimizing customer costs by providing uninterrupted power delivery, and protecting the shareholders who have invested in the utility. Properly used, dissolved gas analysis can provide a powerful continuous monitoring tool in a transformer maintenance program. However, the effectiveness of dissolved gas analysis is limited by the ability to properly disseminate the results of the dissolved gas analysis. Thus, what is needed is a technique for the effective dissemination of dissolved gas analysis data.